Towards development of a performance standard for ...

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Towards development of a performance standard for assessing the effectiveness of wall-window interface details to manage rainwater intrusion Lacasse, M. A.; Cornick, S. M.; Rousseau, M. Z.; Manning, M. M.; Ganapathy, G.; Nicholls, M.; Plescia, S.

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Journal of ASTM International, 6, 9, pp. 1-28, 2009-10-01

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T ow a rds de ve lopm e nt of a pe rform a nc e st a nda rd for a sse ssing t he e ffe c t ive ne ss of w a ll-w indow int e rfa c e de t a ils t o m a na ge ra inw a t e r int rusion

NRCC-50032 Lacasse, M.A.; Cornick, S.M.; Rousseau, M.Z.; Manning, M.M.; Ganapathy, G.; Nicholls, M.; Plescia, S.

February 2010

A version of this document is published in / Une version de ce document se trouve dans:

Journal of ASTM International, 6, (9), pp. 1-28, October 01, 2009, DOI: 10.1520/JAI101446

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M. A. Lacasse 1 , S. M. Cornick1, M. Rousseau1, M. Armstrong, G. Ganapathy1, M. Nicholls1, S. Plescia 2

Towards Development of a Performance Standard for Assessing the Effectiveness of Wall-Window Interface Details to Manage Rainwater Intrusion

REFERENCE: M. A. Lacasse, S. M. Cornick, M. Rousseau, M. Armstrong, G. Ganapathy, M. Nicholls and S. Plescia, “Towards Development of a Performance Standard for Assessing the Effectiveness of Wall-Window Interface Details to Manage Rainwater Intrusion”, Journal of ASTM International (JAI) Vol 6 ABSTRACT: Laboratory water spray testing identifies the performance of a component or assembly under a specified set of simulated wind-driven rain conditions. Well-developed water spray test protocols can also help identify were an assembly is vulnerable to water entry, the test loads at which water entry occurs, and whether the water entry is managed by the installation details in such a way that it does not result in within-wall damage. This paper presents a proposed laboratory test protocol for assessing the effectiveness of wall-window interface details with regard to management of rainwater, and provides a rationale for a performance-based approach to the evaluation method. An overview of the test approach is provided and details of the test apparatus and test specimen are given, including information on implementation of the test method. Examples of testing performed according to the proposed protocol are provided. Finally additional tests for evaluating the performance of installation details are suggested. The additional tests are for field evaluation of installation details, and for laboratory evaluation of installation details with regard to the risk of condensation along window frames. KEYWORDS: installation details, laboratory testing, performance test, rainwater intrusion, wall-

window interface, watertightness,

1. National Research Council Canada, Institute for Research in Construction, 1200 Montreal Road, Building M-20, Ottawa, ON, K1A 0R6 Canada; Michael A. Lacasse, Senior Research Officer 613-993-9715 / [email protected] 2. Canada Mortgage and Housing Corporation, Housing Technology, 700 Montreal Road Ottawa, ON, K1A 0P7

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Introduction The issue of water penetration associated with window installations has been a recognized concern for decades. In the United States prior to the establishment of the International Code Council, (which superseded the three regional model code writing agencies), each of the regional model codes (the Uniform Building Code, the Basic Building Code and the Standard Building Code) promulgated that exterior openings be flashed so as to “be weatherproof”, “be leak proof”, or “prevent entrance or water”. The regional codes each promulgated essentially the same general requirement; none of them however provided guidance concerning what constituted an adequate level of leak resistance, nor did they address how an adequate level of leak resistance might be attained. In Canada, the National Building Code (NBCC) has consistently required protection from precipitation at openings through wall assemblies and in particular the requirement for flashing at the window head. However these performance requirements are likewise provided in general terms similar to those given by the Codes bodies in the United States. The most recent NBCC 2005 edition nonetheless provides significantly more guidance information regarding protection from precipitation relative to past editions. Whereas the NBCC provides the basic guidance on protection from precipitation, such guidance does not constitute a substitute for accepted good practice. In Canada, the CMHC * has often been a useful resource for guidance concerning construction practice. Documents regarding window installation were published by CMHC in the mid to late 80’s [1, 2]. The information provided in these documents largely concerned windows of traditional design, and thus did not address installation of windows with mounting flanges (often termed “nail-on” windows). Flanged windows were increasingly being installed in wood frame buildings in the late 80’s and the (often inadequate) methods by which they were installed led to a number of construction defect investigations [3]. It was not until the 1990’s that issues relating to water penetration at windows began to be addressed by practitioners in North America [4, 5]. Concerns over water penetration led to the development of an ASTM window installation standard in 2001 [6]; revisions of the standard were issued in 2004 and 2007. The ASTM standard, in any of its versions, states that it “places greater emphasis on preventing or limiting rainwater leakage

* CMHC – Canada Mortgage and Housing Corporation

2

than on any other single performance characteristic.” The ASTM standard, even in its most recent form [7], is however, (by the admission of its developers), an imperfect document, and in need of continued refinement. Unresolved issues concerning installation details for windows remain. Ongoing concern relating to water penetration associated with window installation methods is reflected in the state of California’s recent sponsorship of investigations concerning the level of risk associated with different window installation methods. The work undertaken by Leslie [8, 9] concerned evaluation of installation details pertaining to flanged vinyl windows installed in wood frame walls clad with stucco. Laboratory evaluations nominally permitted evaluating the ability of the different installation methods and use of different components to permit adequate drainage to the exterior of the assembly. The evaluations identified conditions under which observable liquid water leaked to the interior when the test assembly was subjected to simulated rain and leakage events. The work concluded that when windows leak, additional design elements are necessary to manage the water entry. Given the unpredictable amounts of and locations for water entry, pan sill drainage was considered essential. Additionally, it was found that an effective interior air barrier is required around window perimeters. Finally, in regard to testing, it was suggested that performance standards are needed for assessing the performance of window installations in different wall assemblies that are “realistic” and supported by field data and “validated models” [9]. In Canada, the utility of the CSA standard specification for windows [10] has recently been brought into question. Ricketts [11, 12] focused on assessing the watertightness of windows and the wall-window interface on behalf of CMHC * . Results indicated that the two principal paths for problematic water leakage are associated with the wall-window interface. The principal paths (Figure 1) were found to be through the window assembly to the adjacent wall assembly (path L4), and through the window to wall interface with the adjacent wall assembly (path L5). The risk associated with leakage via these two paths reflects that moisture within the stud space of the wall cannot readily be dissipated (by either drainage or evaporation), and therefore is likely to cause damage. Water that moves through the window assembly and is visible on the interior (paths L1 to L3 in Figure 1) may cause damage to interior finishes, but is less likely to cause damage to components within the wall. Ricketts [12] indicated that the criteria for water penetration addressed in the CSA A440 specification [10] is unlikely to address leakage via the L4 path, and will not address leakage via the L5 path. An estimate of the * CMHC – Canada Mortgage and Housing Corporation

3

applicability of the test procedure cited in CSA A440 to detect leakage via the different leakage paths is provided in Figure 1; the Figure indicates that the leakage paths posing the greatest risk of consequential damage are insufficiently addressed by the test methodology cited in the standard. Moreover, this standard concerns selection of the units themselves; it does not address installed performance, which is of ultimate importance. Some recommendations that followed from the reports [12, 12] included: •

Assessment of in-service and micro-exposure (at window proximity) conditions

•

Provision for redundancy in water penetration control through the installation of sub-sill drainage.

•

Consideration of the durability of water penetration control performance

•

Development of a water penetration testing protocol for the window to wall interface

Figure 1 – Schematic of water entry points following Ricketts [11]. Given the level of interest in window performance and installation details, the Institute for Research in Construction (IRC) undertook work to assess the capacity of different wall-window interface installation details to manage rainwater intrusion. Several publications have been produced of selected results [13, 14, 15, 16]. The work primarily focused on window installations typical of North American low-rise wood frame construction; this work at the IRC is continuing.

4

The investigations undertaken at the IRC provided a basis for proposing a standardized approach to the performance evaluation of window installations in a laboratory setting. This paper provides a rationale for the proposed approach, details on the implementation of the test method, and information regarding instrumentation of specimens. Brief examples of testing performed following the protocol are provided. These examples are for test specimens representative of typical low-rise wood frame construction. The test protocol can also be adapted to commercial installations. Additionally, proposals for standard tests directly related to the proposed air and watertightness test protocol are offered; such tests include assessing the risk of condensation along window frames for given installation details, and a method for the evaluation of installation details in the field.

Approach to Evaluating Water Management of Window Interface Details Performance Assessment Through Testing It is useful to draw linkages between performance and durability, given that performance assessments are useful in helping ensure the durability or long-term performance of an assembly. Indeed, durability implies satisfactory performance of the basic functions of a wall and its components when subjected to environmental loads and other factors that may have a deteriorating or degrading effect [17]. However, the useful life of a material or component always relates to the particular combination of environmental factors to which it is subjected, so that durability must always be related to the particular conditions involved [18]. When consideration is given to assessing the performance of the assembly, it evidently is dependent on the performance of individual wall components. Hence, it is necessary to understand how wall components as well as wall assemblies respond to the range of climatic conditions to which they will be exposed. However, the manner in which the continuity of building envelope is implemented at junctions and penetrations such as windows, ventilation ducts, electrical outlets and pipes, is necessarily important. Unquestionably, the long-term performance of the assembly depends on providing functional details at these vulnerable points of the assembly [19, 20]. Hence to achieve functional performance of the assembly, the installation details themselves must meet a similar degree of acceptable performance as the components incorporated in the assembly Laboratory water spray testing establishes the degree to which a component or assembly performs under a given set (or given sets) of test conditions. Laboratory water spray testing also helps to determine the location of 5

vulnerable points in a wall assembly. If testing is conducted at a number of different loads, the loads at which water entry either occurs or does not occur can be identified. A test protocol may furthermore be designed so as to discern water entry than can be managed, from water entry that will result or is likely to result in damage. For purposes of this manuscript, laboratory spray testing performed according to a well-developed protocol is termed “performance testing”. Performance testing may be used to relate the response of a test specimen to specific details under loads that simulate design conditions in a specified climate. Results derived from performance tests may provide useful insights for estimating the long-term performance of products when combined with knowledge of in-service conditions and information on the performance of similar products in the field.

Current Weathertightness Standards

In North America, the preeminent standard specification that addresses the weathertight performance of fenestration is the North American Fenestration Standard - Specification for windows, doors, and skylights [21]. This standard was developed jointly by the AAMA * , WDMA † and the CSA ‡ . The North American Fenestration Standard (NAFS) defines watertightness testing requirements for windows according to four performance classes designated R, LC, CW, and AW. The class descriptions are given in Table 1. The test method referenced in NAFS is ASTM E331-00 [22]. The differential air pressures at which water penetration resistance tests are performed are based on the design pressure (DP) associated with the performance grade, where the minimum test pressure for R, LC, and CW windows is specified as being 15% of the DP, and for AW windows is specified as being 20% of the DP. The standard further specifies the minimum water penetration resistance test pressure as 140 Pa (2.9 psf) and the maximum test pressure as either of 580 Pa (12.0 psf) (for U.S. applications), or 730 Pa (15.0 psf) (for Canadian applications). The term “water penetration” is defined narrowly in ASTM E331; water that passes inward beyond a plane defined by the innermost edges of the fenestration unit’s frame is classified by the standard as “water penetration”. Given this narrow definition of “water penetration” water that leaks through a unit’s frame and enters the wall below the unit would not be deemed “water penetration” unless the water happened to also spill to the interior of the wall (past the vertical plane defined by the innermost edges of the unit’s frame).

t

e

Table 1 — S u m m a r y r e l a t i n g t o s t i n g p r o v i d

o f i n w a t e r e d i n (NAFS) [21]

f t

o r m a t i o n i g h t n e s s North American Fenestration Standard

*

AAMA American Architectural Manufacturers Association; Window and Door Manufacturers Association; ‡ Canadian Standards Association †

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Product Specification

Test method for window watertightness

Water penetration resistance test pressure Pa (psf) R** LC CW AW

AAMA/WDMA/CSA 101/I.S.2/A440-08

ASTM E 331-00 Standard Test Method for Water Penetration of 140 180 220 390 Exterior Windows, Skylights, Doors, and Curtain (2.9) (3.75) (4.5) (8.0) Walls by Uniform Static Air Pressure Difference ** Window performance class R: Commonly used in one- and two-family dwellings; design pressure (DP): 720 Pa (15.0 psf) Commonly used in low-rise and mid-rise multi-family dwellings and other buildings where larger LC: sizes and higher loading requirements are expected; DP: 1200 Pa (25.0 psf) CW: Commonly used in low-rise and mid-rise buildings where larger sizes, higher loading requirements, limits on deflection, and heavy use are expected; DP: 1440 Pa (30.0 psf) Commonly used in high-rise and mid-rise buildings to meet increased loading requirements and limits AW: on deflection, and in buildings where frequent and extreme use of the fenestration products is expected; DP: 1920 Pa (40.0 psf) Existing standard test methods for evaluating the weathertightness of installed fenestration include AAMA 501 [23], AAMA 504 [24], and ASTM E1105 [25]. AAMA 501 [23] relates primarily to testing of curtain walls, storefronts, and sloped glazing. Given that this paper primarily concerns qualifying the installation of fenestration in low-rise wood frame construction, AAMA 501 largely concerns installations outside this paper’s scope. AAMA 504 [24], which is the “Voluntary Laboratory Test Method to Qualify Fenestration Installation Procedures”, references ASTM E331 together with other test methods. This method, in contrast to ASTM E331, calls for identification of water penetration between the window perimeter and the rough opening (or, more specifically, lack thereof). The performance criterion for this method regarding watertightness requires that no water penetration be evident through the installation system or into the wall cavity around the fenestration product perimeter at the specified test pressure. The utility of ASTM E1105 [25], is primarily to determine the resistance of fenestration units to water penetration. The scope section of the standard indicates that the test method “can also used to determine the resistance to penetration though joints between the assemblies and the adjacent construction,” but the means by which this might be accomplished are not outlined in the standard. Moreover, the definition of “water penetration” in ASTM E1105 is identical to that in ASTM E331, and thus is narrow. The proposed test protocol outlined in this manuscript more closely approximates AAMA 504 than any other standard test method. Although AAMA 504 specifies a minimum test load and suggests that more severe loads can be applied to the test specimen, it does not outline means for adjusting test conditions to simulate climate loads. Additionally, it does not outline means for measuring water penetration via various paths through the assembly. The test method specifies that test specimens be subjected to “durability cycling,” the assumption being that assemblies will or 7

should essentially retain watertightness after the durability cycling. In contrast, it can be argued that the watertightness of all components and assemblies will eventually deteriorate, and thus that robust installation procedures will by definition accommodate some degradation of watertightness of the components or assemblies. The test protocol being proposed in this manuscript follows this line of reasoning, specifically that deficiencies in watertightness of components and assemblies will eventually occur. Estimating the long-term performance for new or innovative products is challenging, given the need to obtain results in a time frame considerably smaller than the expected life of the product. Key elements to consider when developing performance test protocols include: •

Understanding the behaviour of component parts of an assembly in relation to the performance of the system. This also involves;

•

Consideration of performance of products when installed according to in-service conditions;

•

Knowledge of environmental loads and the manner in which these affect the assembly or components; specifically, having information on the intensity, duration and frequency of occurrence of key climate parameters affecting the assembly.

In this manner, interfaces of adjacent products are delineated, details defined, and in-service conditions estimated. On the basis of test results, key elements that help ensure the long-term performance of the component or assembly can be recognized.

Overview of Approach The proposed test protocol is intended to provide information on whether different window installation details can adequately manage rainwater intrusion. It provides quantitative information on the degree to which the various approaches manage rainwater in relation to simulated climate loads. Under the protocol, the range of loads may be selected as being representative of “design” loads for the region or locale of interest. Hence information on the primary test parameters is provided in which the basis for the selection of values for test conditions is given. Thereafter, information is given on the test apparatus and generic configuration of the specimen. The proposed protocol is adaptable to different types of assemblies. It can be carried out by many test facilities that currently perform watertightness tests. 8

In regard to the configuration, mention is made of the overall size, the location of the window specimen and details regarding the test set-up. As indicated previously, an inherent part of the protocol is the assumption that over time windows will leak and given that there is leakage, the wall-window installations details should be designed and implemented such that inadvertent water entry is contained and drained to the exterior of the assembly. To verify that this is achieved, and the capacity of the installation design to manage water entry at different test loads, deficiencies are purposely introduced in the window assembly thus permitting water entry to the sill area; this is further described in the generic description of the test specimen. Two important aspects of the approach are that water entry be observed and be quantified. To meet these goals the test specimens incorporate transparent sheathing components, (to permit observation of water presence behind the sheathing membrane), and means for collection and measurement of water that penetrates between the window and the rough opening, and of water that leaks into the stud cavity.

Primary Test Parameters—The key climatic factor that affects the severity of a wall assembly’s exposure to water that may penetrate the assembly is the wall’s exposure to wind-driven rain. Although drying potential after rain events also has an effect on the long-term performance of the wall, wind-driven rain is the factor that influences water penetration. Knowing the intensity, duration and frequency of rainfall along with coincident wind conditions at a locale provides a means of characterizing wind-driven rain exposure at the locale. As regards simulation of wind-driven rain in laboratory testing, the two primary test parameters are air pressure difference and water spray rate. Combinations of pressure differential and water spray would ideally be based on known climate parameters. Pressure differentials during spay testing correspond to wind speeds coincident with rain, whereas water spray rates correspond to rainfall rates. If the likelihood of occurrence of values of both wind speed coincident with rain fall and rainfall rates are known for specific climate regions, then one can assess the extent to which window-wall systems attaining specific performance levels might perform in a given region. The selection of a specific set of differential pressure and water spray rate combinations would permit establishing the level of performance at which assemblies can function. The proposed protocol involves subjecting specimens to different levels of simulated wind-driven rain of increasing severity, such that the limit below which systems can adequately perform can readily be determined. From the test protocol then, a specified window-wall assembly is subjected to specific combinations of simulated wind-driven rain by application of pressure differentials across the wall assembly and water spray onto the cladding. The set of combinations is chosen such that these encompass the range of values of simulated wind-driven rain that might be expected to occur at the geographic location within a specified return period. A notional set of test combinations is provided in Table 2; these were derived from a review of wind-driven rain events in North America as reported by 9

Cornick and Lacasse [26]. Spray rates may vary between 0.4 and 3.4 L/min.-m2 and pressure differentials between 75 and 1000 Pa. Rates of water penetration at no pressure differential (0) are also determined to help understand the effects of water entry when the force of gravity alone is acting. Such effects would be evident when water cascades onto window-wall interfaces from adjacent building elements in the absence of a significant pressure differential (i.e. 80 ml/min) relative to the water spray load on the specimen (0.8 to 3.4 L/min-m2) are clearly evident. It can also be seen that collection rates increase with increasing pressure difference and that rates of entry of different assemblies (i.e. A and W) can also be differentiated.

*

Water deposition load Sr(x) at height, x, from top of wall, Sr (x) = (x/h)·2Sr; where h is height of wall; Sr is average spray rate (L/min.-m2) over wall height. 21

Water Spray – Full Spray

Water Spray - Cascade

h

Sr

Sr Water Spray Rate (L/min.-m2), simulating rainfall deposition

Actual nominal water deposition rate along height of wall, h Water load due to vertical migration

Figure 6 –Difference in relative water load along height of specimen when applying full-spray as compared to cascade water deposition loads on cladding Figure 8 provides an example of test results, showing how the rate of water collection for drainage from the sill area below each of two installed windows (each in the same test specimen) related to spray rate and to pressure differential across the specimen. Collection rates in this example ranged from as low as approximately 10 ml/min to rates substantially in excess of 1000 ml/min. Collections rates in this instance were largely insensitive to applied pressure differential but were highly dependent on water deposition (spray) rate.

22

Window Water Entry - 08 ABS 100

90

A

W

08

08

BDTI W1

80

Water Entry (ml/min)

70

60

50

40 W-Window - 08 Spray

30

W-Window - 16 Spray W-Window - 34 Spray

20

A-Window - 08 Spray 10

A-Window - 16 Spray A-Window - 34 Spray

0 0

100

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Chamber Pressure (Pa)

Figure 7 – Rate of water collection at window in relation to pressure differential across specimen; variations in collection rates in relation to the rate of water spray load on the specimen are clearly evident; collection rates increase with increasing pressure difference; rates of entry between different assemblies, A and W, are also evident Reservoir Water Entry - 08 ABS 1400

CMHC Wall 4 08 ABS No Modifications

V

B

1200

Water Entry (ml/min)

1000

800

600

400 B-side Reservoir - 08 Cascade B-side Reservoir - 16 Cascade

200

B-side Reservoir - 34 Cascade V-side Reservoir - 08 Cascade V-side Reservoir - 16 Cascade

0 0

100

200

300

400

500

600

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800

V-side Reservoir - 34 Cascade

Chamber Pressure (Pa)

Figure 8 – Rate of water collection for drainage from sill in relation to pressure differential across specimen; variations in collection rates in relation to the rate of water spray on the specimen are evident; collection rates are not dependent on pressure difference but on water spray loads; similarities between rates of entry of different assemblies, V and B, are also evident. 23

Proposed Related Tests Additional tests that relate to evaluation of window installation methodology are worthy of consideration, specifically a field test for evaluation of installation methods, and a test to determine the risk of condensation associated with a given set of installation details. Notional aspects related to the completing each of these tests are provided below. Field Test Parameters for field testing can be derived from the laboratory test protocol, and could be applied in-situ once a window installation method has been tested in the laboratory. Requirements for such a test would be similar to that for other field tests, such as that provided in: ASTM E1105 [25] (Field Determination of Water Penetration of Installed Exterior Windows by Uniform or Cyclic Static Air Pressure Difference) or ASTM C1601 [27] (F

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Risk to Window Condensation at the Window Frame Depending on the types of windows used and the wall construction into which windows are installed, there evidently are various possible methods for providing drainage; drainage methods are likely to vary primarily with regard to cladding type. The various drainage details may affect air leakage through the assembly. The provision of adequate 25

thermal protection at the window-wall interface, as is currently recommended in building practice, may contradict recommended (or required) details for moisture management. Some approaches to window installation chosen with regard to their ability to manage water penetration may thus raise the risk of formation of condensation on the windows. Hence there is a need to determine if, under cold weather conditions, the approaches do in fact pose a potential for problematic condensation. There exist a number of standard laboratory test methods for determining the potential for the formation of condensation on windows, e.g. ASTM C1199-00 Standard Test Method for Measuring the Steady-State Thermal Transmittance of Fenestration Systems Using Hot Box Methods [28], and AAMA 1503-98 Voluntary Test Method for Thermal Transmittance and Condensation Resistance of Windows, Doors and Glazed Wall Sections [29]. The essential elements of the methods, briefly described, consist of testing a window assembly in a hot (i.e. room-side, interior) and cold (i.e. exterior) box environmental chamber across which there is a specified temperature differential (e.g. 70˚F; ca. 38˚C), measuring the window and frame surface temperatures at specified locations on the window, and calculating a weighted average of the interior surface temperature on the window. If from testing the window, the estimated room-side surface temperature on the window is less than a specified dew point temperature (selected to be representative of “normal” indoor conditions) then condensation on the window is expected. Existing test methods for evaluation of condensation potential of windows could be adapted for evaluating the relative risk of condensation associated with various window installation methods. The test results are likely to be most meaningful when performed on wall assemblies that include cladding systems. As well, one may be able to adapt the test methods to determine the effects of air infiltration on the potential for window condensation for specific installation details. The extent to which windows actually perform when installed is not well understood irrespective of the fact that the same windows may have been subjected to rigorous testing and evaluation following commonly used standard practice to evaluate thermal performance. Tests that help evaluate the risk of condensation at the window frame given specified installation details may prove useful in offering a more complete solution to the window installation conundrum.

26

Conclusion A protocol for a laboratory test method on assessing the watertightness performance of window installation details is proposed. Information is provided on the specimen configuration, tests parameters, instrumentation, and performance criteria. Examples have been provided for the implementation of this test protocol, and the interpretation of test results from the examples have been discussed. Finally, information is a provided regarding additional proposed test methods for evaluation of window installation details, specifically a notional field test and a test for assessing the risk of condensation at the window frame.

Acknowledgements The authors are indebted to Mr. Charles Carll for his thorough review of, many useful suggestions for, and keen effort in the preparation of this paper. The work carried out in the Wall-Window Interface consortium project was partially funded by the Canada Housing and Mortgage Corporation, Public Works and Government Services Canada, Building Diagnostic Technologies, DuPont Weatherization Systems, and the National Research Council Canada. The Extruded Polystyrene Association (XPSA) has also provided support for this work outside the consortium project. The authors would also like to extend their appreciation to others that contributed to this effort, in particular, Mr. Stacey Nunes, Mr. Alex Jacob and Mr. Christopher Short.

27

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